Methods utilizing adsorption to separate fluid mixtures are used commercially, for example, on fixed beds of granulated activated carbon or zeolite. It is believed that a majority of the prior art methods suffer from the drawback of being either a cyclic or batch process, in which the sorbent charge is depleted and must be replaced or regenerated after some use. For systems requiring continuous separation, a spare bed must be available for use during regeneration which often means a duplicate bed and nearly a doubling of capital cost for the separation.
One attempt to solve the problem of fixed beds is to utilize a continuous process such as the Dow Traveling Ion Exchange Bed or a rotating annular chromatograph as described in 30(5) AIChE J 705 (1984). Inherent in any continuous sorptive separation process is the use of a mechanism for moving the sorbent between the sorbing and desorbing (sorbent regeneration) zones. This aspect of sorptive separation was described in U.S. Pat. Nos. 4,548,802 and 4,548,803 which were entitled "Continuous Flow Separation With Moving Boundary Sorption". Math modeling studies of the processes described in these patents reveal it to be approximately competitive with current fixed bed processes. The modeling indicated that increased separation effectiveness would be achieved to the extent that boundary sorptive surface increased.
An effort to achieve greater sorptive surface than possible under the constraints of the moving boundary concept described in said patents led to the new and more comprehensive process concept of this invention. The process of this invention abandons the use of sorbent boundary-forming elements.
Standard sorbent materials have vast surface area per unit mass with smallest pore sizes in the nanometer range. This means that the sorbent atoms or molecules can attach sorbate molecules on almost a one-to-one basis. The drawback to use of these materials is that nearly all (99.999% or more depending on particle size) of the sorbent surface (sites) are internal. Time is required for the sorbate to get to these sites through the necessarily restrictive pores; desorption is similarly retarded so that removal of large or bulky molecules is not practical. As a consequence, sorptive beds are sized on the basis of providing enough holdup for the sorbate to diffuse to empty internal sites before leaving the bed. This results in relatively large beds or low flow rates compared to the case of equivalent external sorptive surface.
Since an external surface could be quickly saturated, it is practically mandatory that it be regenerated on a high frequency basis to take advantage of its accessibility advantage over porous sorbents; continuous regeneration is optimal allowing the minimum sorber size for a given application.
It is recognized that a means of preparing a mixture of solution of prescribed concentration, such as a pharmaceutical preparation, could be effected by the sorptive process. Likewise contacting fluid (say in the desorption zone) with a permanent catalyst-sorbent, or with reactant carried from the sorption zone--as a sorbate--could provide a means of controlling the rate of a chemical reaction, by controlling the sorbent velocity. Consequently, the invention is recognized in its most general aspect as a contactor which could, with appropriate modification, be used for any process in which change results from continuous sorptive treatment of a fluid by a solid.
It is therefore a principal object of the invention to provide an improved process for contacting components of a fluid mixture.
A further object of the invention is to provide a continuous process for contacting components in a fluid mixture with a reversibly swellable sorbent material, which is passed (unswollen) into a sorption or desorption zone so that the sorbent material, after passing through the zone, will swell to promote transfer of one of the components of the mixture to or from the sorbent material.
It is a further object of the invention to provide a continuous process for separating components of a fluid mixture wherein a swellable sorptive material is utilized which has the ability to swell to increase its sorptive transfer rate. The material will be such that de-swelling (removal of nonsorbed fluid components) will be accomplished by passage through the compression seal at the zone boundary.
These and other objects will be apparent to those skilled in the art.